This project is centered around developing a molecular understanding of several key aspects of adaptive thermogenesis, especially brown fat differentiation, expression of uncoupling proteins (UCPs) and the biogenesis of mitochondria. This work is highly relevant to obesity and associated diseases like diabetes (NIDDM) and cardiovascular disorders because the dissipation of energy through thermogenesis is a key component of energy homeostasis in all mammals.Specifically, we have cloned a novel transcriptional coactivator (PGC-1) for PPARgamma and other nuclear receptors that is highly expressed in brown fat, muscle and a few other tissues. Notably, it is dramatically induced upon exposure of mice to the cold and increases the transcriptional activity of PPARgamma and the thyroid receptor on the UCP-1 enhancer. Ectopic expression studies in cultured adipoctyes suggest that PGC-1 can also regulate key genes of mitochondrial biogenesis and/or function. We will extensively explore the biological function of PGC-1 through ectopic expression in a variety of cell types, especially precursors of white fat and muscle. We will assay the ability of this molecule under a variety of hormonal stimulations to activate characteristics of brown fat differentiation and/or other components of thermogenesis: expression of UCPs and the expression of mitochondrial components. This cultured cell work will be complemented by an analysis of transgenic mice utilizing both "gain of function": and knock-out technologies. Key questions here will be: can PGC-1 expression cause "transdifferentiation" of white fat to brown fat, and increase energy dissipation through fat tissues or muscle? Knock-out studies will address the requirement for PGC-1 in adaptive thermogenesis in response to either cold exposure or caloric excess through high fat diets. Structure-function analysis of the PGC-1 molecule will address the nature of its interaction with the nuclear receptors and the biochemical activities it may use to turn on gene expression. Finally, the interesting tissue distribution of PGC-1 expression provides impetus to study how PGC-1 is expressed in brown but not white fat and how it is induced in the cold. As we learn more from these studies concerning the physiological role of PGC-1, the ability to understand and manipulate expression of this gene may take on greater importance.